Method of treating aluminum alloys



' ish is desirable.

Patented Nov. 11, 1941 "1YVLQIHODOETREATINGALUMINUMIAILOIS'. 5 v I f Lima. A. Nook; Jr... imam, nd e -Kell r; Newllensington, Pa., assignorsto Aluminum compa y of America, Pittsburgh la a cor;

poration of Pennsylvania *1 Application Octoberltl Serial No. 300,658

' 'N'o Drawing.

, v '1 Claims.

This invention: relates: to methods. certain aluminum base alloys employed in making of treating.

articles which' will receive an .v-artiflcial oxide coating, and more particularly relatesto, the treatment-of the alloys to improve-their appearance when 'so coated'.".flThe expression aluminum'basealloys as used-herein refers to alloys.

which contain at least 75' per cent aluminum.

By" various chemical andelectrochemical processes known-inthe art-for example, those described in U. "s. Patents 113659.058, and 1,900,472- aluminum and aluminum basealloy surfaces may be provided with an" artiflciallyproduced coating which consists substantially of aluminum oxide, and whichis generally referred to as'an oxide coating. Such oxide coatings are ofappreciable elements just mentioned (which elements and.

compounds are referred to hereinafter as substantially undissolved components), are provided with an artificially produced oxide coating, whether that coating be produced by a chemical treatment or by an electrochemical treatment,

,their surface frequently presents a non-uniform appearance, characterizedby an irregular pattern of light and dark areas, with the result that the surface has a streaked appearance. Such a streaked appearance is objectionable when the metal is used for purposes where a uniform fln- By the expression non-heat treatable aluminum base alloys," as used above and hereinafter, is meant aluminum base alloys which are not susceptible of having their strength substantially improved by a solution heat treatment or by precipitation hardening after a solution heat treatment.

It is;an object of our invention to prevent or reduce a streaked appearance in oxide coated surfaces of non-heat treatable aluminum base alloys which contain a substantially undissolved component. It is a further object of our invention to provide a method of treating non-heat treatable aluminum base alloys which contain a substantially undissolved component, which method will We have found that streaks in artificially oxide 56 bas a loys contalni sa ub tnti lylundis elnpemturebe assoc i coated sfir a sbi was rats mp en can-- emr veat dan educed .519, mpl hi h s. z sulta h al p m imple a 1 erably be h at d-innit,

tempera ure of, nc e t fus on-:01 the. me a an then cooledto; the, normal hot working tempe I ture and hotworked, Although itpreferabl subjec t e od t th mshit mnqratur ment-just mentioned; before anyhotyo ,g done, the high temperature treatment m "y ifolloyyr a hot working step. For example, it is possible to heat the metal to the normal hot working tem-vperature and complete any preliminary hot,, w c rkv ing operations in. the usual manner,v and then employthe high temperaturetreatment followed by a final hot work operation'a's abofve described. However, ,it is preferable that only one hot' working operation follow the high temperature treatment herein described. Subsequent ,to the hot working operation which follows the high temperature treatment, the body may be further; worked by cold rolling or by any other cold working process to produce the desired final shape which is to receive the artificially produced oxide coating. The benefit of the high temperature treatment persists in the material whether or not itundergoes further fabrication by cold working. The material may also be subjected to an annealing treatment at the temperatures commonly used for that purpose and then cold worked without detrimental eifect.

In addition to containing a substantially undissolved component, the metal may also contain other relatively insoluble elements, such as chromium, titanium, zirconium," molybdenum, nickel, or tungsten, and it may also contain soluble ingredients in amounts insufficient to produce precipitation hardening. Examples of non-heat treatable aluminum base alloys which contain a substantially undissolved component, and which are beneficially aflected by the treatment described, are those alloys composed of aluminum and from 0.5 to 3 per cent manganese, with or without iron and silicon impurities to a total of between 0.1 and *1 per cent; or aluminum and from 0.5 to 2.5 per cent man anese, and from 0.25 to 2 per cent magnesium, with or without iron and silicon impurities to a total of between 0.05 and 1 per cent; or aluminum and from 0.5 to 2.5 magnesium, from 0.1 to 2 per cent-zinc, and from 0.05 to 0.25 per cent copper, plus iron and silicon impurities to a total of between 0.05 and 0.50 per cent; or aluminum and from 1 to 3 per cent magplus iron and silicon impurities to a total of between 0.1 and 0.35 per cent. Within the ranges given, the iron and silicon usually combine to 'form a substantially insoluble component. Likewise, the iron sometimes combines with other al- The aluminum base alloy body which is subjected to the elevated temperature may be in the form'of an ingot or billet, or in any other form which is adapted for hot working. Generally, the

most efficient practice is to heat the metal in f ingot form because the heating step which is 3 necessary to prepare the metal for hot working may thereby be combined with the high tem-, i perature treatment. The maximumtemperature j to which the metal may be heated will vary in the operation of my process, since the temperature of incipient fusion differs in various alloys. However, it is necessary to use a temperature of at 9 least 1100 F. in order to obtain the desired re- 1 sults. varies, depending upon such factors as the mass 3 of theanaterial bing treated, theintemalstruc ture, and the composition of the alloy. In the 1 case of a-metalof compara vely thin section, for

The duration of the heating step also example 1 inch, 'a period 2 hours is ordinarily sufficient to prevent any substantial streaking of the oxide coated article; whereas with thicker bodies of metal, it may be necessary to heat them for as long as 10 hours or more to obtain the same results.

In performing the hot working operation I which follows the heating step, any type of working process may be used, as, for example, rolling, forging, pressing, or extruding. The hot working temperature to which the metal should be 'cooledfollowing the heating step will vary with the particular type of working operation employed and the composition of the alloy. For

, nesium, and from 0.1 to 0.75 per cent chromium,

; loying constituents to form insoluble compounds.

825 F., whereupon it was rolled into slab form.

The slab was subsequently annealed and cold rolled to the desired gauge. When the material was given an electrolytically produced oxide coating by making it the anode for minutes in a 15 per cent solution of sulfuric acid at 70 F. and at a current density of 12 amperes per square foot of surface, the surfaces were found to be substantially free of streaks and to have auniform appearance.

In another instance, an ingot of an aluminum base alloy composition of 1.25 per cent manganese, iron and silicon impurities to a total 4 of about 0.5 per cent,and the balance aluminum was heated at a temperature slightly above 1200" F. for 2 hours, allowed to cool in air to 900 F., and was then hot rolled to slab form. When cold rolled sheet produced from this slab was oxide coated in the manner stated in the preceding paragraph, the surfaces of the metal had a uniform, unstreaked appearance.

We claim:

1.- In the art of making artificially oxide coat- I ed aluminum base alloy articles; a method for example, in the rolling of an aluminum base alloy containing 1.25 per cent manganese and 1 per cent magnesium, a temperature of about 825 F. is used. In the case of an aluminum base alloy containing 1.25 per cent maganese, the rolling temperature range is about 800 to 900 F., and the usual extrusion temperature range is 700 to 950 F.

Various methods known in the art for cooling hot metal may be used to cool the metal to the hot working temperature, since the rate of cooling is not critical, but it has been found that it is satisfactory to cool the heated body in air, and that method is preferred. It is essential, nevertheless, that the body be cooled to at least a temperature at which hot working can be satisfactorily, performed.

I Although the best results are obtained if the heated metal is worked before it has cooled below the hot working temperature, beneficial results may also be secured even though the metal is permitted to cool to room temperature and is then reheated to bring it to the working temperature. However, it is preferable that the metal not be permitted to cool below about 650 F. following the high temperature treat- 5 merit Tmd'prior to hot working.

and allowed to cool 'in air'to a temperature of the production of oxide coated surfaces substantially devoid of irregular light and dark areas or streaks comprising the steps of heating at a temperature of at least 1100 F. a body of a non-precipitation-hardening aluminum base alloy containing at least one substantially undissolved component, but below the temperature of incipient fusion of the alloy, for a period of one to ten hours, cooling said body to at least a temperature at which it can be hot worked, hot working said body, and subsequently artificiall'y oxide coating said body.

2. In the art of making artificially oxide coated aluminum base alloy articles, a method for the production of. oxide coated surfaces substantially devoid of irregular light and dark areas or streaks comprising the steps of heating at a temperature of at least 1100 F. a body of an non-precipitation-hardening aluminum base alloy which contains at least one substantially undissolved component, but below the temperature of incipient fusion of the alloy, for a period of one to ten hoursfcooling said body to at least a temperature at which it :can be ;hot worked, but above 650 F., thereafter hot working said body, and subsequently artificially oxide coating said body.

3. In the art of making artificially oxide coated aluminumbase alloy articles, a method for the production of oxide coated surfaces substantially devoid of irregular light and dark areas or streaks comprising the steps of heating at a temperature of at least 1100 F. a body of a non-precipitation-hardening aluminum base alloy which contains at least one substantially undissolved component, but below the temperature of incipient fusion of-the alloy, for a period of one to ten hours, cooling said body to the hot working temperature, hot working said body, and subsequently artificially oxide coating said body. 4. In the art of making artificially oxide coated aluminum base alloy articles, a method for the production of oxide coated surfaces substantially devoid of irregular light and dark. areas or streaks comprising the steps of heating a body of an aluminum base-alloy containing from 0.5 to 2.5 per cent magnesium, from 0.1 to 2 per cent ,zinc, from 0.05 to 0.25 per cent copper, and

from 0.05 to 0.5 per cent iron and silicon, the balance being substantially all aluminum, said heating operation being conducted at a temperature of at least 1100 F., but below the temperature of incipient fusion of the alloy, for a period of one to ten hours, cooling said body to a temperature above 650 F., hot working said body, and subsequently artificially oxide coating said body.

5. In the art of making artificially oxide coated aluminum base alloy articles, a method for the production of oxide coated surfaces substantially devoid of irregular light and dark areas or streaks comprising heating a body of an aluminum base alloy containing from 0.5 to 3 per cent manganese, the balance being substantially all aluminum,. said heating operation being conducted at a temperature of at least 1100 R, but below the temperature of incipient fusion of the alloy, for a period of one to ten hours, cooling said body ,to temperature above 650 F., hot working said body, and subsequently artificially oxide coating said body.

6. In the art of making artificially oxide coated aluminum base alloy articles, a method for the production of oxide coated surfaces substantially 'devoid of irregular light and dark areas or streaks comprising heating a body of an aluminum base alloy containing from 0.5 to

2.5 per cent manganese and from 0.25 to 2 per cent magnesium, the balance being substantially all aluminum, said heating operation being conducted at a temperature of at least 1100 F., but below the temperature of incipient 'fusion of the alloy, for a period of one to ten hours, cooling said body to a temperature above 650 F., hot working said body, and subsequently artificially oxide coating said body.

7. In the art of making artificially oxide coated aluminum base alloy articles, a method for the production of oxide coated surfaces substantially devoid of irregular light and dark areas or streaks comprising heating a body of an aluminum base alloy containing from 1 to 3 per cent magnesium, from 0.1 to 0.75 per cent chromium, and from 0.1 to 0.35 per cent iron and silicon, the balance being substantially all aluminum, said heating operation being conducted at a temperature of at least 1100 F., but below the. temperature of incipient fusion of the alloy, for a period of one to ten hours, cooling said body to a temperature above 650 F., hot working said body, and subsequently ar- 5 tificially oxide coating said body.

JOSEPH A. NOCK, JR. FRED KELLER. 

